Environmental controls on stomatal conductance in a shrub of the humid tropics

Enhanced photosynthetic activity in Spinacia oleracea by spectral modification with a photoluminescent light converting material

The spectral conversion of incident sunlight by appropriate photoluminescent materials has been a widely studied issue for improving the efficiency of photovoltaic solar energy harvesting. By using phosphors with suitable excitation/emission properties, also the light conditions for plants can be adjusted to match the absorption spectra of chlorophyll dyes, in this way increasing the photosynthetic activity of the plant. Here, we report on the application of this principle to a high plant, Spinacia oleracea. We employ a calcium strontium sulfide phosphor doped with divalent europium (Ca0.4Sr0.6S:Eu(2+), CSSE) on a backlight conversion foil in photosynthesis experiments. We show that this phosphor can be used to effectively convert green to red light, centering at a wavelength of ~650 nm which overlaps the absorption peaks of chlorophyll a/b pigments. A measurement system was developed to monitor the photosynthetic activity, expressed as the CO2 assimilation rate of spinach leaves under various controlled light conditions. Results show that under identical external light supply which is rich in green photons, the CO2 assimilation rate can be enhanced by more than 25% when the actinic light is modified by the CSSE conversion foil as compared to a purely reflecting reference foil. These results show that the phosphor could be potentially applied to modify the solar spectrum by converting the green photons into photosynthetically active red photons for improved photosynthetic activity.

Estrogenic and serotonergic butenolides from the leaves of Piper hispidum Swingle (Piperaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Our previous work has demonstrated that several plants in the Piperaceae family are commonly used by the Q'eqchi Maya of Livingston, Guatemala to treat amenorrhea, dysmenorrhea, and pain. Extracts of Piper hispidum Swingle (Piperaceae), bound to the estrogen (ER) and serotonin (5-HT7) receptors.

AIM OF THE STUDY

To investigate the estrogenic and serotonergic activities of Piper hispidum extracts in functionalized assays, identify the active chemical constituents in the leaf extract, and test these compounds as agonists or antagonists of ER and 5-HT7.

MATERIALS AND METHODS

The effects of the Piper hispidum leaf extracts were investigated in estrogen reporter gene and endogenous gene assays in MCF-7 cells to determine if the extracts acted as an estrogen agonist or antagonist. In addition, the active compounds were isolated using ER- and 5-HT7 receptor bioassay-guided fractionation. The structures of the purified compounds were identified using high-resolution LC-MS and NMR spectroscopic methods. The ER- and 5-HT7-agonist effects of the purified chemical constituents were tested in a 2ERE-reporter gene assay in MCF-7 cells and in serotonin binding and functionalized assays.

RESULTS

Three butenolides including one new compound (1) were isolated from the leaves of Piper hispidum, and their structures were determined. Compound 1 bound to the serotonin receptor 5-HT(7) with IC(50) values of 16.1 and 8.3 microM, respectively, and using GTP shift assays, Compound 1 was found to be a partial agonist of the 5-HT(7) receptor. The Piper hispidum leaf extracts, as well as Compounds 2 and 3 enhanced the expression of estrogen responsive reporter and endogenous genes in MCF-7 cells, demonstrating estrogen agonist effects.

CONCLUSIONS

Extracts of Piper hispidum act as agonists of the ER and 5-HT(7) receptors. Compound 1, a new natural product, identified as 9,10-methylenedioxy-5,6-Z-fadyenolide, was isolated as the 5-HT(7) agonist. Compounds 2 and 3 are reported for the first time in Piper hispidum, and identified as the estrogen agonists. No inhibition of CYP450 was observed for any of these compounds in concentrations up to 1 microM. These activities are consistent with the Q'eqchi traditional use of the plant for the treatment of disorders associated with the female reproductive cycle.

Leaf area controls on energy partitioning of a temperate mountain grassland

Using a six year data set of eddy covariance flux measurements of sensible and latent heat, soil heat flux, net radiation, above-ground phytomass and meteorological driving forces energy partitioning was investigated at a temperate mountain grassland managed as a hay meadow in the Stubai Valley (Austria). The main findings of the study were: (i) Energy partitioning was dominated by latent heat, followed by sensible heat and the soil heat flux; (ii) When compared to standard environmental forcings, the amount of green plant matter, which due to three cuts varied considerably during the vegetation period, explained similar, and partially larger, fractions of the variability in energy partitioning; (iii) There were little, if any, indications of water stress effects on energy partitioning, despite reductions in soil water availability in combination with high evaporative demand, e.g. during the summer drought of 2003.

The ecophysiology of early angiosperms

Angiosperms first appeared during the Early Cretaceous, and within 30 million years they reigned over many floras worldwide. Associated with this rise to prominence, angiosperms produced a spectrum of reproductive and vegetative innovations, which produced a cascade of ecological consequences that altered the ecology and biogeochemistry of the planet. The pace, pattern and phylogenetic systematics of the Cretaceous angiosperm diversification are broadly sketched out. However, the ecophysiology and environmental interactions that energized the early angiosperm radiation remain unresolved. This constrains our ability to diagnose the selective pressures and habitat contexts responsible for the evolution of fundamental angiosperm features, such as flowers, rapid growth, xylem vessels and net-veined leaves, which in association with environmental opportunities, drove waves of phylogenetic and ecological diversification. Here, we consider our current understanding of early angiosperm ecophysiology. We focus on comparative patterns of ecophysiological evolution, emphasizing carbon- and water-use traits, by merging recent molecular phylogenetic studies with physiological studies focused on extant basal angiosperms. In doing so, we discuss how early angiosperms established a roothold in pre-existing Mesozoic plant communities, and how these events canalized subsequent bursts of angiosperm diversification during the Aptian-Albian.

Modelling seasonal and diurnal dynamics of stomatal conductance of plants in a semiarid environment

Seasonal and diurnal stomatal conductance, leaf transpiration, and soil water contents of two shrubs of Hippophae rhamnoides L. subsp. Sinensis Rousi and Caragana korshinskii Kom., two trees of Malus pomila Mill. and Robinia pseudoacacia L., and a forb, Artemisia gmelinii, were measured in field of the semiarid Loess Plateau, north China, during the growing season of 2002. We developed a dynamic, nonlinear semi-mechanistic model to relate stomatal conductance of these plants to soil water potential, incident photon flux density, vapour pressure deficit, and partial CO₂ pressure, on leaf surface. The model can be easily adapted to ecosystem simulation because of its mathematical simplicity. Guard-cell osmotic pressure at zero light intensity, apparent elastic modulus of guard cells per leaf area, half-saturation light intensity, maximum light-inducible osmotic pressure, soil-to-leaf resistance at zero plant water potential, sensitivity of soil-to-leaf resistance to xylem water potential, and plant body water capacitance, are independent parameters of the model. The model was fitted to the field data of the five species with a non-linear least-square algorithm to obtain the parameters. The result indicates that the model explained, on average, 88% of seasonal and diurnal variation of stomatal conductance for the five species, in comparison with 67% of variation explained by an early model without plant body water capacitance. Comparisons of the physiological parameters among the species show that the woody species exhibited more tolerance for water stresses than the forb because of their higher dark osmotic pressure, greater capability of seasonal and diurnal osmotic regulation, and stiffer guard cell structure (or smaller stomatal density or both). A decreasing trend of soil-to-leaf resistance from the trees to the shrubs to the forb was found in this study. Midday depression of transpiration and stomatal conductance may or may not occur, depending on the magnitude of body water capacitance.

In situ observation of stomatal movements and gas exchange of Aegopodium podagraria L. in the understorey

Observations of stomata in situ while simultaneously measuring CO(2) gas exchange and transpiration were made in field experiments with Aegopodium podagraria in a highly variable light climate in the understorey of trees. The low background photosynthetic photon flux density (PPFD) caused a slight opening of the stomata and no visible response to sporadic lightflecks. However, if lightflecks were frequent and brighter, slow opening movements were observed. Small apertures were sufficient to allow maximal photosynthetic rates. Therefore, the small apertures observed in low light usually only caused minor stomatal limitations of lightfleck photosynthesis. The response of stomata to step-wise changes in PPFD under different levels of leaf to air vapour pressure difference (Delta(W)) was observed under controlled conditions. High Delta(W) influenced the stomatal response only slightly by reducing stomatal aperture in low light and causing a slight reduction in the initial capacity to utilize high PPFD levels. Under continuous high PPFD, however, stomata opened to the same degree irrespective of Delta(W). Under high Delta(W), opening and closing responses to PPFD-changes were faster, which enabled a rapid removal of the small stomatal limitations of photosynthesis initially present in high Delta(W) after longer periods in low light. It is concluded that A. podagraria maintains a superoptimal aperture in low light which leads to a low instantaneous water use efficiency, but allows an efficient utilization of randomly occurring lightflecks.